Numerical Evaluation of Energy Absorption of Crashworthy Structure for Railway’s Rolling Stock: Application of Damage Mechanics Model

Abstract

The energy absorption of a crashworthy structure for railway’s rolling stock was studied experimentally and numerically. A quasi-static compression test was conducted using a full-scale mockup of a crashworthy structure constructed with welded aluminum alloys. To predict the experimental results, a finite element (FE) simulation was conducted in which the Gurson-Tvergaard-Needleman (GTN) model, representing the accumulation of ductile fractures by the nucleation, growth and coalescence of micro-voids, was employed as the constitutive equations of the parent aluminum alloys and welded regions. A simulation employing the Von-Mises yielding model as the constitutive equations was performed as a conventional approach to demonstrate the advantages of the simulation using the GTN model in predicting the energy absorbing ability. The predictions of the GTN model simulation were proved to be in better agreement with the experimental data than those of the simulation based on the Von-Mises model. The relationship between the total energy absorption and the local phenomena observed in the compression test is discussed.

Evaluation of Energy Absorption of Crashworthy Structure for Railway's Rolling Stock (Numerical Simulation Applying Damage-Mechanics Model)

“…This section describes conformation of the crashworthy structures and the experimental results of the mockup test. Since the details of the mockup tests have already been indicated in previous papers (4), (6) , essential points of the test are described here.…”

“…In a conventional plastic-mechanics model, the Von-Mises yielding condition is employed and the effect of the accumulation of damage in the material is not included. Equation (6) with the values indicated in Table 3 was also applied as the stress-strain relationship in the plastic-mechanics model. Equivalent plastic strain was employed as the fracture criterion of this model.…”

“…Since fracture initiation and propagation degrade the structural stiffness and strength, the fracture region must be limited to as small an area as possible for efficient energy absorption. From this viewpoint, accurately predicting the local fractures and properly evaluating the effect of the fractures on energy absorption are substantially important for designing a crashworthy structure (6) .…”

“…In this research, numerical simulations using FEA were conducted to evaluate the energy-absorbing properties of two different types of crashworthy structures obtained from quasi-static compression tests using the mockups of the structures that have been reported in the previous research (4), (6) . Both structures consisted of welded aluminum alloys: one was composed of stiffened frame structure and thin plates (6) and the other of thin plates and energy-absorbing devices made of extruded aluminum alloy (4) . In the numerical simulation, as constitutive equations of the aluminum alloys and the welding materials, two different material models were employed: a damage-mechanics model and a conventional plastic-mechanics model based on J 2 flow theory.…”

Evaluation of Energy Absorption of Crashworthy Structure for Railway's Rolling Stock (Numerical Simulation Using Damage-Mechanics Model)

“…材料の破断ひずみは，応力三軸度に依存して変化することが知られている (5) ．衝撃吸収構造では，溶接部や応 力集中部において応力三軸度が高くなりやすく，部材の塑性変形に伴って破断が発生することがある．破断の発 生は衝撃吸収構造の剛性や強度の低下を引き起こすため，エネルギ吸収の観点からは破断領域を出来る限り小さ くすることが望ましい．したがって，衝撃吸収構造の設計段階において，破断の発生を正確に予測し，エネルギ 吸収特性に与える影響を適切に評価することが重要となる (6) ． そこで本研究では，構成の異なる 2 つの衝撃吸収構造を対象として，準静的な圧潰を模擬した数値シミュレー ションを実施し，既報 (4), (6) において示した実機試験体を用いた圧潰試験の結果を評価した．衝撃吸収構造はどち らも溶接構造であって，一方は強固なフレーム構造と薄板で構成された構造 (6) であり，他方は薄板とエネルギ吸 収用の押出形材で構成された構造 (4)…”